The present invention relates to systems and methods for removing contaminating gases from water and more particularly, to a system and method for removing radon from water by bubbling the radon gas out of the contaminated water.
The presence of the radioactive gas radon has been found in water supplies of New England and elsewhere in the world. Radon is a colorless, odorless, radioactive gas produced from the natural decay of uranium. In outdoor air, radon is diluted and not recognized as a health hazard. However, when radon gas is trapped indoors in air or water, in sufficiently high concentrations, it can be dangerous. Radon has been shown in several epidemiological studies to be a very potent carcinogen that causes lung cancer in humans.
Uranium, and therefore radon, is frequently found in granite bedrock deposits, which are common throughout the United States and the world. Radon typically enters a home along with the water from a bedrock well. Because radon is a volatile gas, it is given off by the water during common household activities such as bathing, showering, and washing dishes. Thus, the radon given off by the water becomes an inhalation hazard within a home or other building. The EPA has estimated that, on an average annual basis, each 10,000 pico-curies per liter (pCi/L) concentration of radon in the water supply will translate into an indoor air concentration of 1 pCi/L for homes having average air exchange rates. Currently, acceptable concentrations of radon are considered to be in the range of 300 to 4000 pCi/L. The contamination of drinking water with volatile organic chemicals, such as benzene, vinyl chloride and MTBE, has also recently become recognized as a serious health problem.
Different methods and systems have been developed to remove radon and other contaminating gases, such as volatile organic chemicals, from water. One such system is referred to as decay storage and comprises a large baffled water storage tank. Since radon has a radiological half-life of only 3.785 days, simply holding the contaminated water in a storage tank for approximately a month will greatly reduce the radon level. One problem with this type of decay storage is that it requires a large tank and is not suitable for use in a home where space may be limited.
Another example of decay storage requires accumulation of the radon on an absorbent material such as activated carbon. Since the radon decays relatively rapidly, the concentration of radon on the absorbent bed will initially increase, and then gradually reach an equilibrium with the influent radon concentration in the water. One disadvantage with this type of system is that the absorbent bed give off radioactivity, primarily in the form of gamma rays, as the radon decays, which may itself present a health hazard. A second disadvantage is that it is difficult to legally dispose of the radioactive carbon filter when it becomes fouled by other water-borne contaminants such as iron, sediment or bacteria.
Another method is known as spray aeration, for example, as disclosed in U.S. Pat. No. 4,371,383. In spray aeration systems, numerous cycles of spraying are required to achieve the desired removal efficiency. As a result, a relatively large spray tank would be required to provide a sufficient quantity of treated water for use in the home.
According to other methods, water is distributed through a tank while air is blown through the tank in a different direction than the water, for example, as disclosed in U.S. Pat. Nos. 4,869,832; 5,614,086; and 5,045,215. Because the water path is different than the air movement, the flow rates through these devices are limited in order to maintain the designed air/water contact without bypassing the aeration process. In U.S. Pat. No. 5,045,215, for example, water is sprayed onto a perforated tray 12 with air blown separately up through the perforated tray. Baffles 16 are used to direct the water flow and prevent back-mixing and cross-mixing of the froth, thereby achieving the desired air/water contact. If the water flow rate is increased beyond a certain point, however, the water will overflow the baffle 16 and the desired air/water contact will be bypassed. Blowing too much air will cause a similar result.
U.S. Pat. No. 5,614,086 has similar limitations. A series of double baffles is used to create a channel for cascading water flow. The water is aerated as it passes over and under the baffles. If the water or air rate is increased to a certain point, the water might overflow the baffles and not follow the desired flow path, causing the air/water contact to be bypassed. Thus, the systems and methods disclosed in both of these patents have an inherent limit on the flow rate.
Moreover, the available systems for removing radon often cannot easily be installed into the existing water system in a home. Systems such as those disclosed in U.S. Pat. Nos. 5,045,215 and 5,614,086 utilize external pump systems for pumping decontaminated water to a desired location and thus require a large amount of floor space and greater set-up installation time and effort. These devices, also typically incorporate complex control panels that must be installed and wired, increasing costs and requiring a specialized electrical hook-up.
Accordingly, there is a need for a system for removing radon or other contaminating gases that can easily be installed in a home, for example, without requiring an excessive amount of space. There is also a need for a system and method in which the air/water contact is directly proportional and will not be by-passed, even when the flow rate is increased. There is also a need for a method of removing radon or other contaminating gases from water that is efficient enough to remove the necessary amount of gas while being capable of higher flow rates because of a forced aeration or flow path.
A system for removing contaminating gases from contaminated water comprises a tank for holding decontaminated water and having a gas outlet for venting the contaminating gases removed from the contaminated water. A bubbling container is fluidly coupled to the tank such that decontaminated water flows from a top region of the bubbling container into the tank. A duct is at least partially disposed within the bubbling container with a first end of the duct positioned proximate a bottom region of the bubbling container. A second end of the duct is coupled to a source of contaminated water for introducing the contaminated water to the bottom region of the bubbling container.
In a preferred embodiment, a spraying connection, such as a nozzle/venturi, sprays the water into the second end of the duct. A blower is also coupled to the second end of the duct for blowing air into the duct as the contaminated water is introduced therethrough, thereby further aerating the contaminated water. At least one diffuser is positioned within the bubbling container for breaking up and further mixing the aerated contaminated water with the air. The aerated contaminated water rises to the top region of the bubbling container where the contaminating gases bubble out of the aerated contaminated water. According to one example, the diffuser includes one or more perforated grids disposed within the bubbling container. A pump pumps the decontaminated water from the tank.
The system preferably includes a control system for stopping the introduction of contaminated water and the blowing of air into the duct when the decontaminated water in the tank reaches a predetermined level. The control system preferably includes a normally closed valve coupled between the supply of contaminated water and the duct. The normally closed valve is opened when the decontaminated water is below the predetermined level. The control system further includes a float switch within the tank for switching off a power supply to the blower and to the normally closed valve when the decontaminated water in the tank reaches the predetermined level.
The present invention also features a method of removing contaminating gases from contaminated water. The method comprises the steps of supplying the contaminated water and introducing air together with the contaminated water into the bottom region of the bubbling container such that the air and the contaminated water flow generally in the same direction into the bubbling container through a forced flow path. The aerated contaminated water is forced to bubble up through the bubbling container to a top region of the bubbling container where the contaminating gases bubble out of the aerated contaminated water leaving decontaminated water to flow out of the bubbling container. The contaminating gases are vented and the decontaminated water is pumped to a desired location.
According to the exemplary method, the contaminating gases include radon, the water supply is a home water supply, and the desired location is a home water system. The method preferably includes the step of stopping the supply of contaminated water and the introduction of air when the decontaminated water in the tank reaches a predetermined level.